This invention relates to dual cycle engines, and more particularly to a dual cycle internal combustion piston engine and method wherein engine coolant and exhaust gases are used to produce steam that is applied to the piston for recovering waste combustion heat.
While the internal combustion engine is depended upon for most land transportation throughout the world, it loses about 72%-75% of the fuel heating value through radiation, engine coolant and exhaust. In one car that was tested, the measured brake horsepower was only 21% of the fuel heating value at 72 mph and only 18% at 43 mph. Meanwhile, increasing fuel prices and shortages mount steadily as world supplies of fossil fuel decline and greenhouse gas emissions continue to rise. The Rankine cycle has been used to recover waste heat from internal combustion engines, but power recovery has been inefficient and has suffered from various other shortcomings. For example, it has been proposed to use coolant heat to power a separate steam turbine which is connected to the crankshaft of the engine. However, steam turbines have not proved efficient in units under 500 HP, have had gear box problems and cannot accelerate rapidly thus making them impractical for use in vehicles such as cars and trucks. Within the engine itself, cooling problems can be caused by an inability to provide coolant capable of robust heat transfer to the feed water or by steam generation hot spots, which may result in an uncontrolled heating condition in certain parts of the engine due to what is known as transition film boiling, a form of runaway heating that follows nucleate boiling often leading to damage from pre-ignition or detonation in the combustion chamber. Consequently, successful waste heat recovery in an IC engine presents unique problems especially if high fuel efficiency is to be achieved together with reliable operation in which there is little likelihood of a burnout or detonation in the combustion chamber. It is, therefore, a general object of this invention to provide an improved dual cycle internal combustion steam engine that is both efficient with respect to the fraction of waste heat that is recovered as well as being reliable in operation.
These and other more detailed and specific object and advantages of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.